SI-7788 Refactoring in typedImplicit1

  - route checks for Predef.conforms through one method
  - handle all the failure cases of `NameLookup` at once
  - Use string interpolation
  - outsource generation of the Ident or Select tree to,
    TreeGen.

More to do in here, but I'm trying at least to leave things
no messier than when I arrived.